import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;


public class BinaryTree {
    static class TreeNode {
        public char val;
        public TreeNode left;//左孩子的引用
        public TreeNode right;//右孩子的引用
 
        public TreeNode(char val) {
            this.val = val;
        }
    }

    /**
     * 创建一棵二叉树 返回这棵树的根节点
     *
     * @return
     */
    public TreeNode createTree() {
        TreeNode A = new TreeNode('A');
        TreeNode B = new TreeNode('B');
        TreeNode C = new TreeNode('C');
        TreeNode D = new TreeNode('D');
        TreeNode E = new TreeNode('E');
        TreeNode F = new TreeNode('F');
        TreeNode G = new TreeNode('G');
        TreeNode H = new TreeNode('H');


        TreeNode root = A;
        root.left = B;
        root.right = C;
        B.left = D;
        B.right = E;
        //C.left = F;
        C.right = G;
        D.left = H;
        return root;
    }
 
    // 前序遍历
    public void preOrder(TreeNode root) {
        if(root == null){
            return;
        }
        System.out.print(root.val+" ");
        preOrder(root.left);
        preOrder(root.right);
    }
 
    // 中序遍历
    void inOrder(TreeNode root) {
        if(root == null){
            return;
        }
        inOrder(root.left);
        System.out.print(root.val+" ");
        inOrder(root.right);
    }
 
    // 后序遍历
    void postOrder(TreeNode root) {
        if(root == null){
            return;
        }
        postOrder(root.left);
        postOrder(root.right);
        System.out.print(root.val+" ");
    }
 
    public static int nodeSize;
 
    /**
     * 获取树中节点的个数：遍历思路
     */
    int size(TreeNode root) {
        if(root == null){
            return 0;
        }
        nodeSize++;
        size(root.left);
        size(root.right);
        return nodeSize;
    }
 
    /**
     * 获取节点的个数：子问题的思路
     *
     * @param root
     * @return
     */
    int size2(TreeNode root) {
        if(root == null){
            return 0;
        }
        return size2(root.left)+size2(root.right) +1;
    }

    /*
     获取叶子节点的个数：遍历思路
     */
    public static int leafSize = 0;
 
    int getLeafNodeCount1(TreeNode root) {
        if(root == null){
            return 0;
        }
        if(root.left==null && root.right==null){
            leafSize++;
        }
        getLeafNodeCount1(root.left);
        getLeafNodeCount1(root.right);
        return leafSize;
    }
 
    /*
     获取叶子节点的个数：子问题
     */
    int getLeafNodeCount2(TreeNode root) {
        if(root == null){
            return 0;
        }
        if(root.left == null && root.right == null){
            return 1;
        }
        return getLeafNodeCount2(root.left)+getLeafNodeCount2(root.right);
    }
 
    /*
    获取第K层节点的个数
     */
    int getKLevelNodeCount(TreeNode root, int k) {
        if(root==null || k<=0){
            return 0;
        }
        if(k == 1){
            return 1;
        }
        return getKLevelNodeCount(root.left,k-1) + getKLevelNodeCount(root.right,k-1);
    }
 
    /*
     获取二叉树的高度
     时间复杂度：O(N)
     */
    int getHeight(TreeNode root) {
        if(root == null){
            return 0;
        }
        int leftHeight = getHeight(root.left);
        int rightHeight = getHeight(root.right);
        return leftHeight > rightHeight ? leftHeight+1:rightHeight+1;
    }

    // 检测值为value的元素是否存在
    boolean find(TreeNode root, char val) {
        if(root == null){
            return false;
        }
        if(root.val == val){
            return true;
        }
        return find(root.left,val) || find(root.right,val);
    }
 
    //层序遍历
    void levelOrder1(TreeNode root) {
        if(root == null){
            return;
        }
        Queue<TreeNode> queue = new LinkedList<TreeNode>();
        queue.offer(root);
        while(queue.peek()!=null){
            TreeNode cur = queue.poll();
            System.out.print(cur.val+" ");
            if(root.left!=null){
                queue.offer(cur.left);
            }
            if(root.right!=null){
                queue.offer(cur.right);
            }
        }
    }

    // 判断一棵树是不是完全二叉树
    boolean isCompleteTree(TreeNode root) {
        if(root == null){
            return true;
        }
        if(root.left == null && root.right != null){
            return false;
        }
        if(root.left == null && root.right == null){
            return true;
        }
        return isCompleteTree(root.left)&&isCompleteTree(root.right);
    }

    public List<List<Integer>> levelOrder(TreeNode root) {
        List<List<Integer>> list = new ArrayList<>();
        if(root == null){
            return list;
        }
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        while(!queue.isEmpty()){
            int size = queue.size();
            List<Integer> temp = new ArrayList<Integer>();
            while(size>0){
                TreeNode cur = queue.poll();
                temp.add(cur.val);
                size--;
                if(cur.left!=null){
                    queue.offer(cur.left);
                }
                if(cur.right!=null){
                    queue.offer(cur.right);
                }
            }
        }
        return list;
    }
}